Blood culturing by the broth culture technique is an important diagnostic tool in modern medicine. It is used to determine difficult to identify infections, especially those which have not responded to treatment by the normally used antibiotics. In the broth culture technique, blood is withdrawn aseptically from a pateint's vein and is added to a blood culture bottle containing a culture medium designed to provide the nutritional and environmental requirements of the bacteria commonly encountered in bacteremia.
Blood is added to a blood culture bottle using either a closed system or an open system. In the closed system, a sterile blood collecting tube is used, permitting blood to enter the bottle directly from the patient. In the open system, blood is collected with a sterile needle and syringe and is either injected into the blood culture bottle at the bedside or the blood specimen is mixed with an anticoagulant for transporting to the laboratory where it is injected into the blood culture bottle.
A conventional sterile blood collecting tube includes a relatively thick walled plastic tube having a needle located at each end thereof. One needle, which is inserted into a patient's vein, is a venipuncture needle, while the other needle is inserted through the pierceable stopper of a blood culture bottle. The needles of a sterile blood collecting tube have cannulas which are anchored in machined metal hubs. The hubs extend into and are anchored in the ends of the plastic tube. Removable plastic sheaths are provided for each needle with the venipuncture needle having a sheath closed at one end, while the sheath for the blood culture bottle needle is open at both ends and contains a wad of sterile cotton.
In using the conventional sterile blood collecting tube, it is necessary for the medical person to squeeze the thick walled plastic tube, either by hand or with a hemostat, to prevent the discharge of blood from the tube during the insertion and removal of the stopper piercing needle from the blood culture bottle. Frequently, during the taking of multiple samples, blood is accidentally discharged from the stopper piercing needle, thus creating hygenic problems in the patient's environment.
The injected culture bottle is vented for aerobic culturing, or is left unvented for anaerobic culturing. The bottle is usually incubated at 35.degree. C. for a period varying from 7 to 21 days. During the incubation time, the bottle is visually inspected, gram-stained and subcultured, using suitable media and incubation conditions in order to determine if the growth of a microorganism has occurred.
The number and frequency of specimen collections is usually based upon the particular clinical situation. Usually, two blood culture bottles, each of which preferably contains 100 ml of a culture medium, should each be innoculated with 5 to 10 ml of blood. One bottle should be vented for aerobic incubation and one bottle should be left unvented for anaerobic incubation. The blood culture bottles customarily contain a soy broth medium and carbon dioxide under negative pressure.
After the blood is injected into the blood culture bottles, it is necessary to vent the bottle used for aerobic incubation. Venting has customarily been accomplished through the use of a sterile disposable 20-22 gauge needle having sterile absorbent cotton packed in the needle hub. The needle is inserted through the rubber stopper in the outlet of the blood culture bottle. This vent permits the introduction of air into the bottle, with the sterile cotton functioning to prevent the entry of airborne bacteria. However, this method has not proved entirely satisfactory since the sterile cotton is not completely effective in preventing the entry of airborne bacteria into the blood culture bottle.
Subculturing has required the use of a sterile needle and syringe with the needle attached to the syringe being inserted through the rubber top of the blood culture bottle to withdraw the required amount of innoculated culture medium.
The blood culture bottle used for anaerobic incubation is not vented under present practice. The bacterial action in the sealed bottle generates gases, resulting in a pressure buildup in the bottle. The pressure may go as high as 80 psi. In addition to the danger of rupture of the bottle, the pressure buildup in an anaerobic bottle prevents subculturing until the pressure is relieved.
The danger of backflow of blood into a patient's vein from an evacuated specimen tube during the taking of multiple blood samples exists under present practice. Because most specimen tubes in use are non-sterile, the reverse flow of blood into the patient presents a serious health hazard.